Automobiles incorporate various electronic devices. Conventionally, wiring harnesses have been used to connect these electronic devices to each other. The wiring harness comprises electric wires and connectors attached to ends of the electric wires. Each of the connectors of the wiring harness is connected to corresponding each of connectors each fixed to cases of the electronic devices, so that these electronic devices are connected to each other.
Meanwhile, in recent years, the connectors of the electronic devices are directly connected to each other as illustrated in FIGS. 3 and 4 without use of the wiring harnesses in view of costs and workability in assembly (for example, see the patent literature PTL 1).
FIGS. 3 and 4 illustrate a waterproof structure 200 in a structure where (a) a connector 201 fixed to a mounting hole 11a of a case 11 of a motor incorporated in an automobile is connected to (b) a connector 202 fixed to a mounting hole 12a of a case 12 of an inverter.
The connector 201 includes a terminal accommodating portion 204 adapted to accommodate a terminal 205, and an outer housing 203 having a shape of a cylinder that opens toward the connector 202, the outer housing 203 fixed to a case 11 and adapted to accommodate therein the terminal accommodating portion 204.
The outer housing 203 includes (a) a cylindrical portion 231 positioned inward of a mounting hole 11a and adapted to accommodate therein the terminal accommodating portion 204, and (b) an overlapping portion 235 extending in a flange-like manner from an end of the cylindrical portion 231 and outward of the cylindrical portion 231, the end being a proximal end with respect to the connector 202.
The overlapping portion 235, which is disposed on and in contact with an outer surface 11b of the case 11, has a shape of a ring surrounding the mounting hole 11a of the case 11. Also, the overlapping portion 235 includes (a) a first groove 235a provided in a concave manner on a surface abutting the outer surface 11b of the case 11 and provided in a ring shape over an entire circumference of the overlapping portion 235, and (b) a second groove 235b provided in a concave manner on a surface abutting the outer surface 12b of the case 12 of the inverter and provided over an entire circumference of the overlapping portion 235.
A first packing 208a is attached into the first groove 235a. Also, a second packing 208b is attached into the second groove 235b. 
The connector 202 includes (a) a terminal 207 adapted to be connected to a terminal 205 of the connector 201 and (b) a connector housing 206 adapted to accommodate the terminal 207 and fixed to the case 12.
In the waterproof structure 200 as illustrated in FIG. 4, the overlapping portion 235 of the connector 201 and the outer surface 12b of the case 12 of the inverter are brought into abutment with each other when the connector 201 is connected to the connector 202, so that the second packing 208b makes waterproof the interface between the overlapping portion 235 and the case 12. Also, the first packing 208a makes waterproof the interface between the overlapping portion 235 and the case 11. In this manner, water indicated by an arrow in FIG. 4 entering a space between the cases 11, 12 is prevented from entering the cases 11, 12 via an interface between the mounting hole 11a and the connector 201 and an interface between the mounting hole 12a and the connector 202, and from entering inner spaces of the connectors 201, 202.